This is been listed on the first bug reports page in the community – created wiki for about a week, so it’s likely the same issue.
http://thingsthataresmart.wiki/index.php?title=Bug:_First_Reports
It was caused by a recent update to how SmartThings handles zigbee.
As far as what you can try on your own, the first thing is to make sure that OTA updates is disabled in the IDE for your account. Then unplug the hub, including taking out any batteries, and leave the hub off power for at least 20 minutes while leaving your other zigbee devices on power. Then put the hub back on power. This will force everything to re-sync.
This has fixed the problem for some people, but not all. So definitely do report it to support.